New vehicle designs and additional accessories require an engine to deliver more horsepower. However, the engine needs a larger crankshaft to provide the additional horsepower. A larger crankshaft requires larger main bearing caps for stabilization. To operate the engine properly, the larger crankshaft and bearing caps must be placed lower in the crankcase. This placement eliminates the previously available space for the oil pump inlet tube.
In a typical engine configuration, an oil pump connects to an inlet tube outside the crankcase. The inlet tube connects to the pick-up tube inside the crankcase or inside the oil pan. The pick-up tube is positioned in the oil pan for pumping oil from the oil reservoir formed by the oil pan. When the engine is operating, oil is pumped from the oil reservoir, through the pick-up tube, through the inlet tube, and into the oil pump.
When the inlet tube is moved outside the crankcase, there are more opportunities for leaks to develop. Leaks also may develop from improperly connected pick-up and inlet tubes. Leaks may develop because the oil pan extends beyond the crankcase. Leaks also may develop because the oil pump inlet tube or the pick-up tube extends through a passage formed in the oil pan. In the later two cases, a gap may form along an edge of the oil pan. This scenario is especially true when the oil pan extends to connect to the engine'front cover. In assembly operations, it is extremely difficult to consistently match the edges of the front cover and crankcase from engine to engine. If the edges of the front cover and the crankcase are uneven, a gap will form when the oil pan is attached.
Leaks also are a greater concern when the oil pump inlet tube is moved outside the crankcase. While no leak is desirable, a leak inside the crankcase at the connection of the inlet and pick-up tubes is less consequential. Such a leak would cause oil to leak into the inlet tube or into the crankcase or oil pan. These leaks would have less impact because the crankcase and oil pan are full of oil during engine operation.
In contrast, a leak outside the crankcase would have an adverse impact on engine performance. Such a leak may cause oil to escape from the engine. While it may not cause an immediate problem, it would harm the engine over the long term. Moreover, a leak may cause air to enter the hydraulic system. Air in the hydraulic system would have a catastrophic impact on engine operation.
To avoid some of these leaks, the pick-up tube and the oil pump inlet tube could be one piece. However, they typically are not one piece because of manufacturing costs. The one piece would stick out of the oil pan or the crankcase. This arrangement has a greater chance of being damaged during transportation of the part and assembly of the engine. The combined tube may be hit and may even snap when the part is shipped or the engine moves through the assembly line. Moreover, a combined tube would not prevent leaks from gaps in the oil pan connections.
Accordingly, there is a need for a direct passage from the oil reservoir to the oil pump in an engine that does not pass through the crankcase.